CUDA Basic Matrix Addition - Large Matrices

Question

Hi all,

I'm trying to add two 4800x9600 matrices, but am running into difficulties...

It's a simple C=A+B operation...

Here is the kernel:

__global__ void matAdd_kernel(float* result,float* A,float* B,int size)
{
        int x=blockIdx.x*blockDim.x+threadIdx.x;
        int y=blockIdx.y*blockDim.y+threadIdx.y;
        int idx=x*y+x;

        if(idx<size)
        {
                result[idx]=A[idx]+B[idx];
        }
}

and here is the code:

void matAdd(Matrix C,Matrix A,Matrix B)
{
        int N=A.w*A.h;
        dim3 dimBlock=dim3(22,22);
        int yBlocks=A.w/dimBlock.y+((A.w%dimBlock.y)==0?0:1);   //yBlocks is 219 for dimBlock(22,22) and 9600x4800
        int xBlocks=A.h/dimBlock.x+((A.h%dimBlock.x)==0?0:1);   //xBlocks is 437 for dimBlock(22,22) and 9600x4800
        dim3 dimGrid=dim3(xBlocks,yBlocks);
        matAdd_kernel<<<dimGrid,dimBlock>>>(C.data,A.data,B.data,N);
        cutilCheckMsg("kernel launch failure");
}

I'm using a Matrix as follows:

typedef struct{
        int w;
        int h;
        float* data;
}Matrix;

And here is the output when I print the top-10 rows and bottom-10 rows:

top-10 rows A:
-0.023930 0.047744 -0.074694 0.053555 -0.032298 0.038762 -0.068890 0.088894 -0.044989 0.005679 -0.054846 0.064743
-0.070026 0.059445 -0.078712 0.001957 -0.050910 0.067603 -0.089646 0.076562 -0.039840 0.052980 -0.074809 0.037390
-0.042785 0.087303 -0.005369 0.017769 -0.075572 0.075981 -0.064457 0.067737 -0.045192 0.046887 -0.030999 0.006888
-0.040708 0.020566 -0.089926 0.082820 -0.010478 0.021086 -0.086581 0.095966 -0.054339 0.068906 -0.060855 0.087460
-0.059717 0.038708 -0.026613 0.053984 -0.088490 0.066764 -0.005617 0.091969 -0.018239 0.097972 -0.073692 0.010064
-0.052374 0.048555 -0.037706 0.043377 -0.071556 0.075888 -0.002523 0.037950 -0.065693 0.078094 -0.011694 0.039196
-0.092799 0.011099 -0.056766 0.091866 -0.059577 0.029236 -0.063502 0.091717 -0.030844 0.079273 -0.087244 0.048310
-0.089582 0.004614 -0.002560 0.058306 -0.006922 0.097391 -0.099892 0.039699 -0.036129 0.038520 -0.084387 0.012408
-0.054143 0.048351 -0.006309 0.002902 -0.073858 0.012903 -0.089030 0.041077 -0.034445 0.030259 -0.071056 0.002762
-0.048605 0.047165 -0.082960 0.096326 -0.066084 0.029297 -0.070599 0.034394 -0.044475 0.075287 -0.063274 0.023137
-0.033560 0.030527 -0.019907 0.078961 -0.052821 0.088959 -0.043210 0.061808 -0.020862 0.058320 -0.028586 0.079149
-0.087878 0.034127 -0.040097 0.092205 -0.033817 0.099641 -0.002590 0.012473 -0.050764 0.093213 -0.065811 0.075233

bottom-10 rows A:
0.006791 -0.015538 0.072625 -0.049761 0.029860 -0.093147 0.023192 -0.031281 0.030545 -0.068470 0.020244
0.014509 -0.057081 0.049269 -0.047556 0.022443 -0.092672 0.065184 -0.030968 0.097352 -0.052493 0.062981
0.004188 -0.028991 0.063084 -0.082578 0.005537 -0.030271 0.038801 -0.043018 0.066686 -0.004677 0.054946
0.013995 -0.011381 0.075888 -0.069206 0.012784 -0.009126 0.068735 -0.066544 0.070738 -0.055201 0.097867
0.083719 -0.007838 0.018854 -0.098974 0.023769 -0.044483 0.028541 -0.032198 0.047691 -0.005788 0.039455
0.066290 -0.033136 0.097825 -0.051469 0.012732 -0.038881 0.076786 -0.069891 0.084848 -0.050189 0.017055
0.077407 -0.088394 0.006851 -0.047383 0.081140 -0.094065 0.002880 -0.072353 0.095627 -0.096577 0.025683
0.023140 -0.008283 0.096901 -0.011595 0.031076 -0.079637 0.050198 -0.014112 0.027430 -0.012270 0.054234
0.011981 -0.053835 0.076015 -0.062570 0.082806 -0.040616 0.030618 -0.003141 0.031599 -0.093869 0.048415
0.065879 -0.060177 0.085832 -0.000699 0.038540 -0.014198 0.018127 -0.013525 0.094031 -0.072898 0.083781
0.056596 -0.090405 0.092818 -0.013577 0.078385 -0.061543 0.053441 -0.092938 0.032074 -0.017903 0.051810

top-10 rows B:
-0.023930 0.047744 -0.074694 0.053555 -0.032298 0.038762 -0.068890 0.088894 -0.044989 0.005679 -0.054846 0.064743
-0.070026 0.059445 -0.078712 0.001957 -0.050910 0.067603 -0.089646 0.076562 -0.039840 0.052980 -0.074809 0.037390
-0.042785 0.087303 -0.005369 0.017769 -0.075572 0.075981 -0.064457 0.067737 -0.045192 0.046887 -0.030999 0.006888
-0.040708 0.020566 -0.089926 0.082820 -0.010478 0.021086 -0.086581 0.095966 -0.054339 0.068906 -0.060855 0.087460
-0.059717 0.038708 -0.026613 0.053984 -0.088490 0.066764 -0.005617 0.091969 -0.018239 0.097972 -0.073692 0.010064
-0.052374 0.048555 -0.037706 0.043377 -0.071556 0.075888 -0.002523 0.037950 -0.065693 0.078094 -0.011694 0.039196
-0.092799 0.011099 -0.056766 0.091866 -0.059577 0.029236 -0.063502 0.091717 -0.030844 0.079273 -0.087244 0.048310
-0.089582 0.004614 -0.002560 0.058306 -0.006922 0.097391 -0.099892 0.039699 -0.036129 0.038520 -0.084387 0.012408
-0.054143 0.048351 -0.006309 0.002902 -0.073858 0.012903 -0.089030 0.041077 -0.034445 0.030259 -0.071056 0.002762
-0.048605 0.047165 -0.082960 0.096326 -0.066084 0.029297 -0.070599 0.034394 -0.044475 0.075287 -0.063274 0.023137
-0.033560 0.030527 -0.019907 0.078961 -0.052821 0.088959 -0.043210 0.061808 -0.020862 0.058320 -0.028586 0.079149
-0.087878 0.034127 -0.040097 0.092205 -0.033817 0.099641 -0.002590 0.012473 -0.050764 0.093213 -0.065811 0.075233

bottom-10 rows B:
0.006791 -0.015538 0.072625 -0.049761 0.029860 -0.093147 0.023192 -0.031281 0.030545 -0.068470 0.020244
0.014509 -0.057081 0.049269 -0.047556 0.022443 -0.092672 0.065184 -0.030968 0.097352 -0.052493 0.062981
0.004188 -0.028991 0.063084 -0.082578 0.005537 -0.030271 0.038801 -0.043018 0.066686 -0.004677 0.054946
0.013995 -0.011381 0.075888 -0.069206 0.012784 -0.009126 0.068735 -0.066544 0.070738 -0.055201 0.097867
0.083719 -0.007838 0.018854 -0.098974 0.023769 -0.044483 0.028541 -0.032198 0.047691 -0.005788 0.039455
0.066290 -0.033136 0.097825 -0.051469 0.012732 -0.038881 0.076786 -0.069891 0.084848 -0.050189 0.017055
0.077407 -0.088394 0.006851 -0.047383 0.081140 -0.094065 0.002880 -0.072353 0.095627 -0.096577 0.025683
0.023140 -0.008283 0.096901 -0.011595 0.031076 -0.079637 0.050198 -0.014112 0.027430 -0.012270 0.054234
0.011981 -0.053835 0.076015 -0.062570 0.082806 -0.040616 0.030618 -0.003141 0.031599 -0.093869 0.048415
0.065879 -0.060177 0.085832 -0.000699 0.038540 -0.014198 0.018127 -0.013525 0.094031 -0.072898 0.083781
0.056596 -0.090405 0.092818 -0.013577 0.078385 -0.061543 0.053441 -0.092938 0.032074 -0.017903 0.051810

top-10 rows C:
-0.047860 0.095488 -0.149388 0.107110 -0.064596 0.077524 -0.137780 0.177788 -0.089978 0.011358 -0.109692 0.129486
-0.140052 0.118890 -0.157424 0.003913 -0.101820 0.135206 -0.179292 0.153124 -0.079680 0.105960 -0.149618 0.074780
-0.085570 0.174606 -0.010738 0.035538 -0.151144 0.151962 -0.128914 0.135474 -0.090384 0.093774 -0.061998 0.013776
-0.081416 0.000000 -0.179852 0.165640 -0.020956 0.042172 -0.173162 0.000000 -0.108678 0.137812 -0.121710 0.000000
-0.119434 0.077416 -0.053226 0.107968 -0.176980 0.133528 -0.011234 0.000000 -0.036478 0.195944 -0.147384 0.000000
-0.104748 0.000000 -0.075412 0.086754 -0.143112 0.151776 -0.005047 0.000000 -0.131386 0.156188 -0.023388 0.078392
-0.185598 0.022198 0.000000 0.183732 -0.119154 0.058472 -0.127004 0.000000 -0.061688 0.158546 -0.174488 0.096620
-0.179164 0.000000 -0.005121 0.116612 -0.013844 0.194782 -0.199784 0.079398 -0.072258 0.077040 -0.168774 0.024816
-0.108286 0.096702 -0.012618 0.005803 -0.147716 0.025806 -0.178060 0.082154 -0.068890 0.060518 -0.142112 0.005524
-0.097210 0.000000 0.000000 0.000000 -0.132168 0.058594 -0.141198 0.000000 -0.088950 0.150574 -0.126548 0.046274
-0.067120 0.061054 0.000000 0.000000 -0.105642 0.177918 -0.086420 0.123616 -0.041724 0.116640 -0.057172 0.158298
-0.175756 0.068254 -0.080194 0.184410 -0.067634 0.199282 -0.005179 0.000000 -0.101528 0.186426 -0.131622 0.150466

bottom-10 rows C:
0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000
0.029018 0.000000 0.000000 0.000000 0.000000 0.000000 0.130368 0.000000 0.000000 0.000000 0.000000
0.000000 -0.057982 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000
0.000000 0.000000 0.151776 0.000000 0.000000 0.000000 0.000000 -0.133088 0.000000 0.000000 0.000000
0.000000 0.000000 0.000000 -0.197948 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000
0.000000 0.000000 0.000000 0.000000 0.025464 0.000000 0.000000 0.000000 0.169696 0.000000 0.000000
0.000000 0.000000 0.000000 0.000000 0.000000 -0.188130 0.000000 0.000000 0.000000 0.000000 0.000000
0.000000 0.000000 0.193802 0.000000 0.000000 0.000000 0.100396 0.000000 0.000000 -0.024540 0.000000
0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 -0.006282 0.000000 0.000000 0.000000
0.000000 -0.120354 0.000000 0.000000 0.000000 -0.028396 0.000000 0.000000 0.188062 0.000000 0.167562
0.000000 0.000000 0.000000 -0.027154 0.000000 0.000000 0.000000 0.000000 0.000000 -0.035806 0.000000

As you can see, C=A+B just isn't working...

It's ok for the top part of the matrix, but goes hay-wire in the bottom half. I have no idea where all those zeros are coming from...

Am I doing something wrong?

Any insight greatly appreciated. Many thanks in advance,

Answer 1

The part of your code that sticks out to me the most is:

int idx=x*y+x;

I believe what you mean is:

int idx=maxX*y + x;

Otherwise, if x=0 and y=1000, then idx=0.

This would also explain why it works for some like y=0 and not for others.

You will need to pass in the maximum X value for your matrix.

Hope that helps!